Arbitrary File Write via Archive Extraction (Zip Slip) Affecting github.com/bblfsh/bblfshd/runtime package, versions *

github.com/bblfsh/bblfshd/runtime is a provides the runtime environment to execute the bblfsh drivers.

Affected versions of this package are vulnerable to Arbitrary File Write via Archive Extraction (Zip Slip). The unsafe handling of symbolic links in an unpacking routine may enable attackers to read and/or write to arbitrary locations outside the designated target folder.

It is exploited using a specially crafted zip archive, that holds path traversal filenames. When exploited, a filename in a malicious archive is concatenated to the target extraction directory, which results in the final path ending up outside of the target folder. For instance, a zip may hold a file with a "../../file.exe" location and thus break out of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.

The following is an example of a zip archive with one benign file and one malicious file. Extracting the malicous file will result in traversing out of the target folder, ending up in /root/.ssh/ overwriting the authorized_keys file:

+2018-04-15 22:04:29 ..... 19 19 good.txt

+2018-04-15 22:04:42 ..... 20 20 ../../../../../../root/.ssh/authorized_keys

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